Internal combustion engines, for example, diesel engines, gasoline engines, or natural gas engines employ turbochargers to deliver compressed air for combustion in the engine. A turbocharger compresses air flowing into the engine, helping to force more air into combustion chambers of the engine. The increased supply of air allows for increased fuel combustion in the combustion chambers of the engine, resulting in increased power output from the engine.
A typical turbocharger includes a housing, a shaft, a turbine wheel attached to one end of the shaft, a compressor impeller connected to the other end of the shaft, and bearings to support the shaft. Exhaust from the engine expands over the turbine wheel and rotates the turbine wheel. The turbine wheel in turn rotates the compressor impeller via the shaft. The compressor impeller receives cool air from the ambient and forces compressed air into combustion chambers of the engine.
Compressors for turbocharger applications must have a wide operating range to account for the variations in operating conditions of the engine associated with the turbocharger. The operational range of a compressor can be defined as the range of pressure ratios between a choke condition and a surge condition. A choke condition occurs when the mass flow rate of air through the compressor reaches a maximum value because of, for example, sonic flow conditions between the compressor blades. A surge flow condition occurs when the mass flow rate of air through the compressor becomes limited due to flow instability caused by, for example, flow separation. A recirculation passage is often provided in the compressor inlet channel to recirculate air and increase the operational range of the compressor.
U.S. Pat. No. 6,945,748 B2 of Svihla et al. that issued on Sep. 20, 2005 (“the '748 patent”) discloses one such recirculation system. In particular, the '748 patent discloses an annular inlet air recirculation channel extending from a first slot upstream of the vanes of the compressor impeller to a second slot downstream of the vanes. The '748 patent discloses that the recirculation channel is formed using an aerodynamic channel ring supported in a smooth annular recess formed in the compressor housing. The '748 patent further discloses that the channel ring is mounted using radial struts connected to the housing. Further, the '748 patent discloses that the channel ring and the channel recess may be machined to form smoothly variable surfaces prior to the assembly of the ring into the housing.
Although the '748 patent discloses a recirculation system, the disclosed recirculation system may still be improved upon. In particular, formation of the recirculation channel of the '748 patent may require extensive machining of the support arms and related surrounding housings to accommodate the ring. Additionally, the arrangement disclosed in the '748 patent may require machining of the struts required to attach the ring to the housing. Further, because the ring is separately machined from the housing, alignment of the ring with the housing to achieve optimal recirculation may be difficult.
The compressor inlet recirculation system of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.